I’m packing my bags for one more trip on Asiana Airlines to Hong Kong via South Korea’s Incheon airport (outside Seoul). Incheon airport was constructed over water about 1-3 meters (3 to 10 feet) deep. These types of airports are inevitably subject to some subsistence. Incheon’s is expected to be about 2.5 cm (1 inch) over the next 20 years. Hong Kong’s airport appears to be the best-engineered marine platform in the world and had hardly budged since 1998. Then there is Japan’s Kansai airport built over the sea 5 km off Osaka at a depth of 17-18 meters (56 to 59 feet). The world’s longest 2-tiered bridge connects it to the city nearby. It sinks 2 to 4 cm 
in any given year, so in 20 years’ time, it may sink 40 to 80 cm (16 to 33 inches). Yikes! .. however, the soil engineers from Osaka University are confident it will not sink completely into the ocean.